The mechanisms involved in the development of the retinal vasculature are still controversial, but in dog and human we have demonstrated that it occurs by vasculogenesis, the differentiation and coalescence of retinal angioblasts. When the developing retinal vasculature is exposed to hyperoxia, severe vasoconstriction and eventual vaso-obliteratidn occurs in the dog model of oxygen-induced retinopathy (OIR). When this severely compromised vasculature is reintroduced to room air, the retina is hypoxic because of an inadequate blood supply and angiogenesis occurs. To understand this susceptibility to hyperoxia and the angiogenesis that ensues, it is necessary to first understand how the retinal vasculature develops and the cells and signals involved. This proposal will address how the superficial retinal vasculature forms using immunohistochemistry in fetal human retinas. This will also be accomplished by in vitro assessment of the molecules that stimulate retinal angioblast chemotaxis (VEGF, ANG2, SDF-1, and SCF) and presence of their putative receptors on the angioblasts. We have recently demonstrated that dog angioblastSiarei,rnultipotent in that they can become endothelial cells or pericyte-like cells. We wish to better understand the stimuli for their differentiation and fate determination in vitro. We will also evaluate the'ability^angioblasts to build a blood vessel in vitro and their ability to contribute retinal vasculogenesis in vivo. -,;.coic[unreadable].;;. Finally, we will employ a novel nonviral gene delivery:system, multilayered magnetic nanoparticles, to control vaso-obliteration and vasoproliferation in thedogsOIR model. Vaso-obliteration will be challenged by using a bioresponse element promoter to turn-on genes that could prevent endothelial cell and angioblast apoptosis in response to hyperoxic insult.-The nanoparticle strategy will also be used to deliver antiangiogenic genes to hyalocytes and proliferating endothelial cells in retinal neovascularization to inhibit angiogenesis. The goal of this proposal is to better understand the development of the retinal vasculature so that we can effectively target both the vaso-obliterative susceptibility and angiogenic response that occurs in OIR and human retinopathy of prematurity. . .;